Galls develop when leaves are sucked by the juveniles; these change into adults that erupt out of the gall: (remember the movie ‘Alien’?)
click here for more psyllid information.
There is a significant lerp infestation on Foxes Lair wandoos at the moment.
When curiosity overcame me and I opened a few to have a look, my eyes encountered maggots instead of psyllids. The maggots are larvae of the gall-midge (in actual fact a Cecidomyidae fly) that produces a salivary substance which forces acacias to produce gall cells. These have replaced flowers making the plant look like it has fruit.